The invention relates to an antenna array for a motor vehicle.
Modern motor vehicles typically have at least one antenna, often even a plurality of antennas and optionally even different types of antennas, in order to be able to use, for example, radio and TV services in motor vehicles. Usually the configuration of the antennas endeavors to reach the best possible compromise between the antenna efficiency, the electromagnetic compatibility with respect to the vehicle's own interfering components and the design of the vehicle. For example, in modern motor vehicles the antennas are often integrated into the rear window, in one of the rear side windows or in the spoiler.
In this context an antenna array that is totally or partially integrated into such a part of the vehicle, for example, the rear window, can include a number of antennas. It can also include additional elements for the antenna(s), for example, connecting elements, amplifiers, filters and/or signal processing units (for example, antenna diversity module). The antenna array can also include structural parts that primarily do not fulfill any antenna function, for example, a rear car window heating system.
However, it is frequently the case that the heating lines of a rear car window heating system also fulfill, besides their heating function, an antenna function. For such heating lines it is known, for example, from WO 2005/060044 A1 to suppress the interference from the vehicle electrical system that is transmitted by the heating current to the heating conductors acting as the antenna by use of modules having a high impedance behavior at high frequencies (so-called blocking circuits or blocking circuit filters), when the antenna connecting point is electrically connected to the heating field. Moreover, it is also possible to suppress in this way, as also applied in the vehicles of the assignee, that the useful currents of the antennas leak off to the supply potential of the power supply and/or to the ground potential.
Working on this basis, the object of the invention is to improve the antenna reception of AM antennas installed in motor vehicles.
This object is achieved by an antenna array for a motor vehicle, the antenna array having at least one AM antenna for receiving at least long wave, medium wave and/or short wave signals, as well as at least one additional electrically conductive structural part that is arranged so as to be adjacent to the AM antenna. The additional structural part is connected to a ground potential and/or supply potential of the motor vehicle by at least one filter element, by which signal frequencies in at least one frequency range that is to be received by the AM antenna are suppressed. Advantageous embodiments and further developments of the invention are described herein.
The invention improves the reception properties of the AM antenna in the long wave, medium wave and/or short wave range. Surprisingly, this technological success is not the result of filter designs that are based directly on the AM antenna itself, but rather on filter designs that are based on an adjacent structural part or component.
Similarly, the invention makes it possible to vary in a targeted manner the characteristic reception properties of the AM antenna in the long wave, medium wave and/or short wave range. For example, it is possible to achieve a gain as a function of the angle of incidence.
In this context, it is contemplated to switch on and/or off an antenna or, very loosely generalized, to vary in a targeted manner its characteristic by shielding an adjacent part.
The AM antennas in the antenna arrays according to the prior art exhibit suboptimal properties with respect to the specific market and/or customer demands. For example, it is usually very important for the North American market that the sound quality of the radio reception be very good in the medium wave range. However, this customer expectation cannot always be fulfilled to the customer's satisfaction with the above described compromise between antenna efficiency, electromagnetic compatibility and vehicle design. This situation applies in particular to regions where the strength of the transmission signal is weak (for example, in rural areas). In that case the physical nature, in particular, the length of the AM antenna that is integrated into the rear car window, the side window or the spoiler, is often inadequate for receiving medium waves.
Moreover, adverse external conditions can make the reception of medium waves problematic and/or reduce its quality. In many cases the motor vehicle does not even have the aforementioned customary installation sites. Similarly, conventional antenna arrays may not be able to satisfy the special market demands on the antenna performance, for example, with unusual frequency bands, field strengths or varying broadcasting station and/or geographical topology.
The invention is especially appropriate for use with AM antennas having a length that is very much smaller than the wavelength of the signals received, because it is precisely in such AM antennas in the conventional antenna array that the aforementioned suboptimal properties and/or drawbacks can occur most often.
The invention is based on the consideration that the reception properties of the AM antenna can be improved by influencing the metallic or otherwise electrically conductive structural parts, which are directly and/or electrically connected at low impedance to the electrical vehicle body and are arranged so as to be adjacent to the AM antenna, in such a manner that the electrical vehicle body, as the ground potential, is no longer “visible” to the AM antenna. In this context, a conductive element is “visible” when it acts on the antenna as a parasitic capacitance. Such parasitic capacitances attenuate the supply of the antenna signal power to the next step of the signal chain, which is often designed as an amplifier. The invention prevents such an attenuation.
In principle, the vehicle body of a structural part adjacent to the AM antenna can be made “invisible” to the AM antenna in an especially easy way by making the adjacent structural part of an electrically non-conductive material, provided that such a design would not impair its function. Similarly, the adjacent structural part can be electrically insulated from the vehicle body, provided that such a measure would not impair its function.
However, the invention provides a targeted shielding of the adjacent structural part for the frequency range to be received by the AM antenna. As a result, the adjacent vehicle body is made invisible in a selective way for such frequencies. Optionally the structural part can be shielded simultaneously against all higher frequencies. Then a low pass filter can be used as the filter element.
The invention can be applied in an especially advantageous way to antenna arrays, in which the heating wires of a rear car window heating system run at least partially in the immediate proximity of the AM antenna. In such cases the improvement in the AM reception that the invention achieves is especially apparent.
Similarly, the invention can be applied advantageously to antenna arrays, in which an additional antenna, for example, an FM and/or TV antenna, is arranged at least partially in the immediate proximity of the AM antenna as an additional structural part in the context of the invention. For example, both antennas can be mounted on the same rear car window. Even in such cases the invention affords a significant improvement in the AM reception.
In order to enhance the effect of the invention, additionally existing low impedance or capacitance ground paths can be eliminated and/or minimized.
This purpose can be achieved, on the one hand, by disposing the structural part, which is shielded according to the invention, at a long geometric distance from the parts, lines or other structural parts that are connected to the ground potential. On the other hand, this purpose can also be achieved by a targeted low impedance and low capacitance design of the additional terminals of the shielded structural part and/or by a targeted low impedance and low capacitance design of the optionally necessary matching circuits of the structural part.
As described above, the additional structural part can be designed as an additional antenna. Preferably this antenna is connected to the ground potential and/or supply potential of the motor vehicle (additionally to the aforementioned filter element), furthermore by way of at least one additional filter element, by which the signal frequencies in at least one frequency range that is to be received by the additional antenna are suppressed. As a result, it can also be prevented that the useful currents of the additional antenna leak off to the supply potential and/or to the ground potential.
According to a preferred embodiment of the present invention, the antenna array exhibits, besides the aforementioned adjacent structural part, at least one additional electrically conductive component, which is arranged so as to be adjacent to the AM antenna, and the filter element has a bifilar coil (bifilar winding) comprising a first and a second coil section.
At the same time the additional structural part is connected to the ground potential and/or supply potential by the first coil section of the bifilar coil. The additional component is connected to the ground potential and/or supply potential by the second coil section of the bifilar coil. In this context the bifilar coil is defined as a two wire coil that is wound counter-clockwise. At the same time each winding wire represents by itself a complete coil, called a coil section herein. When the coil sections are supplied with identical current, the resulting magnetic fields virtually cancel each other out. Therefore, this design makes it possible to suppress the generation of magnetic interference fields.
The additional component, mentioned in the preceding paragraph can also be designed as an antenna, in particular, an FM and/or TV antenna. It can be fitted together with the AM antenna and the additional structural part, which can also be designed as an antenna, in particular, an FM and/or TV antenna, in a rear window of the vehicle.
Especially if the AM antenna, the additional structural part and an additional component (which may or may not be present), of the antenna array are integrated into a rear window of the motor vehicle, it may be advantageous for the at least one filter element, which is used and optionally designed as a bifilar coil, to be mounted on the rear car window shelf or the C post of the motor vehicle.
The invention can be implemented in various ways, some of which have already been addressed and some of which shall be discussed below on the basis of the following embodiments. In addition, other designs for improving the reception quality can be implemented selectively and in stages. In this way a fine scalability is achieved. As a result, the cost per vehicle is recouped only if the corresponding special equipment options are also installed. Hence, a simply equipped vehicle can also be provided with a simple and cost effective antenna system comprising very few parts that have to be installed.
In addition, a reduction in cost can also be achieved by the extensive use of parts that are identical to those used in prior art antenna systems and by the use of standard components. The only requirements for a practical implementation of the invention are minor system interventions and/or new developments.
Furthermore, given a suitable design for all of the country-specific special equipment and for the diverse antenna relevant special equipment options, just a single rear car window is necessary, both with respect to its conductor structure (which can also be used for heating) as well as with respect to the design of its electrical (heating) terminals and antenna taps. This strategy enables cost reductions in the areas of development, logistics and production.
The antenna according to the invention allows for an improvement in the response to customer-specific and market-specific demands. In particular, vehicle users who appreciate high functionality (in particular, good reception power) and who are design sensitive, can be offered a suitable product by way of the invention.
In addition, the invention makes it possible to achieve a reduction in cost, because the functionality of the antenna concept is expanded only selectively in response to the customer and/or market-specific demands and not in general for each product that is produced. The results are advantages, from which production, parts complexity and logistics can also benefit.
Last, but not least, when viewed over the life cycle of a motor vehicle, the invention also increases the flexibility in connection with the varying external conditions of the broadcasting landscape as well as with respect to technical innovations, such as the conversion from analog to digital reception.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.